1. Field Of The Invention
This invention relates to otic prosthesis; more particularly to ossicular replacement prosthesis for the middle ear.
2. Description Of The Prior Art
Reconstruction of the sound-conducting mechanism of the middle ear by surgical implantation of biocompatible prostheses is well known. FIG. 1 of the drawings is a schematic representation of the natural mechanism for transmitting vibrations of the eardrum (tympanum) to the sound-producing organs of the inner ear which are located behind the aperture (oval window) between the middle and inner ears. The mechanism includes three tiny bones called the malleus, the incus and the stapes, which move in response to the vibration of the tympanum. When disease or advanced infection of the middle ear occurs, excessive bone growth around or degeneration of these tiny bones can prevent their movement with a consequent loss of hearing. Hearing may be restored by the removal of two or three of these bones and the surgical implantation of a vibration-transmitting prosthesis.
Ossicular replacement prostheses take two basic forms: (1) When all three bones are removed, the prosthesis must span between the tympanum and the oval window or footplate and thus is called a total ossicular replacement prosthesis. Typically, the prosthesis is a one-piece device having a broad, thin head portion resting against the tympanum and a rigidly connected central shaft portion, which is cut to length by the surgeon, and is used in one of two modes: (a) when the footplate of the stapes is left in the oval window, a small hole is drilled through it for receiving the shaft of the prosthesis, thus assuring a close fit; or (b) if the footplate is removed, a vein, tissue or fascia graft is sized and placed over the oval window and the shaft of the prosthesis is placed in the center of the graft. (2) When only the malleus and incus are removed, and the stapes remains, the prosthesis need only span between the tympanum and the free end (capitulum) of the stapes and thus is called a partial ossicular replacement prosthesis. This device is constructed in the same manner as the total device except that the shaft portion is shorter and typically has either a tubular or inverted cup-shaped end portion which fits over the capitulum of the stapes.
Frequently, the surgeon encounters situations where the surface of the tympanum is not exactly parallel with the surface against which the tip of the shaft portion of the prosthesis must rest or fit into. Because it is important to the success of the implantation that the pressure exerted by the head portion of the prosthesis upon the tympanum be uniform throughout, the surgeon, in such case, will forcibly bend the shaft portion of the device in an attempt to compensate for the difference in angulation. The movable joint of the present invention eliminates the need to bend the the device, which could set up stresses that would cause dislodgment at either end, or penetration of tissue (the tympanum) within the middle ear (called extrusion) as a result of uneven forces set up in the device.